Japanese patent specification JP 2002-081883 describes a heat exchanger comprising heat transfer plates with similar heat transfer plates. In the ensuing text, the term “heat transfer plate” is synonymous with the term “plate”. The plates exhibit a pattern of ridges and valleys extending diagonally across the heat transfer plate. Stacking to form a plate stack entails the plates being placed on one another in such a way that the ridges and valleys of a plate are connected to the ridges and valleys of an adjacent plate via contact points. The mutual orientation of the plates is such that there is mutual divergence of the extent of the ridges and valleys of adjacent plates upon their mutual abutment at said contact points. Mutually adjacent plates are connected via said contact points to form a permanently connected plate stack.
A problem of heat exchangers comprising plates configured according to said patent specification JP2002-081883 is that the contact points round the port regions have a tendency to snap. The term “snap” means the permanent connection between two mutually adjacent plates parting at a contact point. Factors inter alia which influence the degree of risk of a contact point parting are the position of the contact point on the plate and its proximity to other contact points. Round the port regions in the embodiment according to patent specification JP2002-081883, and on many conventional plates, contact points are provided round each port region at different distances from the center of the port region. The result is that the stresses acting at the respective contact points round the port differ because some of the contact points are situated closer to certain contact points than to other contact points. Contact points which are near to one another can thus distribute stresses among them, with the result that the respective contact points will be less affected by said stresses. This means that certain other contact points which are situated round the port regions and are not close to another contact point will therefore have a greater tendency to part than other contact points round the port regions.
A known technique for creating contact points round a port is to press a number of nibs in the region round the port. Said nibs are situated at the same radial distance from the centre of the port. A disadvantage of such an embodiment is that the respective nibs require a large surface to enable them to be pressed in the plate. This means that the plate's heat transfer surface is reduced by the surface devoted to pressing said nibs, with consequent reduction in the heat transfer via said plate.